Super-capacitor with separator and method of producing the same

ABSTRACT

A method of producing a super-capacitor provides a first substrate having a first base, forms a first electrode on the first substrate, and forms a separator so that the electrode is between the first base and the first separator. The method also micromachines holes through the separator, forms a chamber, and adds electrolyte, having ions, to the chamber. The electrolyte is in contact with the first electrode within the chamber. In addition, the holes are sized to permit transmission of the ions of the electrolyte through the holes.

PRIORITY

This patent application claims is a continuation in part of U.S. patentapplication Ser. No. 14/469,004, filed Aug. 26, 2014, entitled, “METHODOF PRODUCING A SUPER-CAPACITOR,” and naming Yingqi Jiang and Kuang L.Yang as inventors, the disclosure of which is incorporated herein, inits entirety, by reference.

REFERENCE TO RELATED PATENT APPLICATIONS

This patent application is related to the following patent applications,each of which is incorporated herein, in its entirety, by reference:

-   -   U.S. patent application Ser. No. 14/593,230, filed Jan. 9, 2015,        entitled, “INTEGRATED CIRCUIT WITH SHARED ELECTRODE ENERGY        STORAGE DEVICES,” and naming Yingqi Jiang and Kuang L. Yang as        inventors,    -   U.S. patent application Ser. No. 14/509,950, filed Oct. 8, 2014,        entitled, “INTEGRATED SUPER-CAPACITOR,” and naming Yingqi Jiang        and Kuang L. Yang as inventors,

FIELD OF THE INVENTION

The invention generally relates to super-capacitors and, moreparticularly, the invention relates to stacked super-capacitors andmethods of forming stacked super-capacitors

BACKGROUND OF THE INVENTION

Although the size of portable electronic devices continues to shrink,their energy requirements often do not comparably decrease. For example,a next-generation MEMS accelerometer may have a volume that is 10percent smaller and yet, require are only 5 percent less power than theprior generation MEMS accelerometer. In that case, more of the MEMS diemay be used for energy storage. Undesirably, this trend can limitminiaturization and applicability of such electronic devices.

The art has responded to this problem by developing chip-levelsuper-capacitors (also known as “micro super-capacitors”), which havemuch greater capacitances than conventional capacitors. Specifically,when compared to conventional capacitors and batteries, super-capacitorsgenerally have higher power densities, shorter charging and dischargingtimes, longer life cycles, and faster switching capabilities.

Super-capacitors sometimes have two closely spaced electrodes that canshort circuit if contact is made. Although the prior art positions aninsulative separator between the electrodes to avoid this problem, manysuch separators cause other problems.

SUMMARY OF VARIOUS EMBODIMENTS

In accordance with one embodiment of the invention, a method ofproducing a super-capacitor provides a first substrate having a firstbase, forms a first electrode on the first substrate, and forms aseparator so that the electrode is between the first base and the firstseparator. The method also micromachines holes through the separator,forms a chamber, and adds electrolyte, having ions, to the chamber. Theelectrolyte is in contact with the first electrode within the chamber.In addition, the holes are sized to permit transmission of the ions ofthe electrolyte through the holes.

Although the holes permit ion transmission, the separator may be formedfrom a material that is substantially impermeable to the ions of theelectrolyte. For example, each hole in a set of the holes of theseparator may have largest dimension (e.g., corner-to-corner or adiameter) of between about 2 nanometers and 5 microns. As anotherexample, the separator may include nitride or parylene, and the firstbase may include low resistivity silicon (e.g., doped silicon). Themethod also may form a current collector on the first substrate. Such acurrent collector may be positioned between the first base and the firstelectrode, and be in electrical contact with the first electrode.

Some embodiments also provide a second substrate supporting a secondelectrode, and wafer bond the first substrate to the second substrate.Insulating material at the bonding area between the two substrates canbe provided to prevent electrical short circuits between the twosubstrates after bonding. As a result of this bonding, 1) the separatorelectrically prevents electrical contact between the first electrode andthe second electrode, and 2) the bonded first and second wafers form thenoted chamber. A micromachining process preferably forms the firstelectrode and separator.

In accordance with another embodiment, a super-capacitor has a firstsubstrate and a second substrate, a first electrode supported by thefirst substrate, and a second electrode supported by the secondsubstrate. The first substrate is wafer bonded to the second substrateto form a chamber. The super-capacitor also has a first separatorbetween the first electrode and the second electrode within the chamber,and electrolyte, having ions, within the chamber. The separator has aplurality of micromachined holes sized to permit the ions of theelectrolyte to pass through the holes. In addition, the electrolyte isin contact with the first and second electrodes.

In accordance with other embodiments, a method of producing asuper-capacitor forms 1) a first electrode on a first substrate, 2) aseparator on the first substrate, 3) holes through the separator, and 4)a second electrode on a second substrate. The method also wafer bondsthe first substrate to the second substrate to form a chamber so thatthe separator is between the first electrode and the second electrode.In addition, the method adds electrolyte, having ions, to the chamber sothat the electrolyte is in contact with the first electrode and thesecond electrode. The holes through the separator are sized to permitthe ions of the electrolyte to pass through the holes.

BRIEF DESCRIPTION OF THE DRAWINGS

Those skilled in the art should more fully appreciate advantages ofvarious embodiments of the invention from the following “Description ofIllustrative Embodiments,” discussed with reference to the drawingssummarized immediately below.

FIG. 1 schematically shows a super-capacitor that may be configured andformed in accordance with illustrative embodiments of the invention.

FIG. 2 schematically shows a cross-sectional view of the super-capacitorof FIG. 1 across line 2-2.

FIG. 3 shows a process of forming the super-capacitor of FIG. 1 inaccordance with illustrative embodiments of the invention.

FIG. 4 schematically shows a cross-sectional view of the super-capacitorof FIG. 1 at step 300 of the process of FIG. 3.

FIG. 5 schematically shows a cross-sectional view of the super-capacitorof FIG. 1 at step 302 of the process of FIG. 3.

FIG. 6 schematically shows a cross-sectional view of the super-capacitorof FIG. 1 at step 304 of the process of FIG. 3.

FIG. 7 schematically shows a cross-sectional view of the super-capacitorof FIG. 1 at step 306 of the process of FIG. 3.

FIG. 8 schematically shows a cross-sectional view of the super-capacitorof FIG. 1 as the process of FIG. 3 approaches step 308.

FIG. 9 schematically shows a cross-sectional view of the super-capacitorof FIG. 1 at step 308 of the process of FIG. 3.

FIG. 10 schematically shows a cross-sectional view of thesuper-capacitor of FIG. 1 as the process approaches step 310 of theprocess of FIG. 3.

FIG. 11 schematically shows a cross-sectional view of thesuper-capacitor of FIG. 1 at step 310 of the process of FIG. 3.

FIG. 12 schematically shows a cross-sectional view of thesuper-capacitor of FIG. 1 at step 312 of the process of FIG. 3.

FIG. 13 schematically shows a cross-sectional view of thesuper-capacitor of FIG. 1 as the process approaches step 314 of theprocess of FIG. 3.

FIG. 14 schematically shows a cross-sectional view of a super-capacitorof FIG. 1 at step 314, 316, and 318 of the process of FIG. 3, but withtwo separators.

FIG. 15 schematically shows another embodiment of the invention.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

Illustrative embodiments use micromachining processes to form robust andreliable super-capacitors. To that end, such embodiments formsuper-capacitors having two out-of-plane electrodes that, within achamber filled with an electrolyte, are electrically and physicallyisolated from each other by a rigid and robust separator. While theseparator may be made from a material that does not permit transmissionof the electrolyte ions therethrough (e.g., nitride), it has a pluralityof micromachined holes with the geometries to permit ion transmission.Accordingly, ions are free to pass through the holes of the separator,permitting relatively free ion movement within the chamber. Details ofillustrative embodiments are discussed below.

FIG. 1 schematically shows a perspective view of a micro super-capacitor(hereinafter “super-capacitor 10”) configured in accordance withillustrative embodiments of the invention. FIG. 2 schematically shows across-sectional view of the super-capacitor 10 along line 2-2 of FIG. 1.Specifically, the super-capacitor 10 is a unitary chip-level devicehaving a pair of multilayer substrates 12 bonded together to form aninterior chamber 16. Among other things, the interior chamber 16contains a pair of stacked electrodes 18 (i.e., out of plane electrodes18 relative to the substrate 12), and electrolyte material 20 (alsoreferred to as “electrolyte 20” that together form a capacitance. Inother words, the electrodes 18 and electrolyte material 20 cooperate tohave the capacity to store a prescribed electrical charge.

To prevent electrical contact between the electrodes 18, the chamber 16also contains a unitary separator 14 that physically separates the twoelectrodes 18. Among other functions, the separator 14 substantiallyprevents the electrodes 18 from making electrical contact. As discussedbelow, the separator 14 preferably is formed from a material that iscommonly used in micromachining, such as nitride, parylene, or an oxide.As such, the separator material is generally impermeable by the ions ofthe electrolyte material 20. Such a design thus would be ineffective ifsolid.

The inventors recognized that a robust separator material is moredesirable than prior art separator material (e.g., polymers), but,unlike prior art separators, such materials are generally impermeable toions. This limitation makes more desirable material impractical.Accordingly, the inventors realized that the separator 14 should havesome means to permit ion transmission and, consequently, formed holes 22through the separator 14. The holes 22 preferably are sized to have aninner dimension/geometry that permits transmission of the ions withinthe electrolyte material 20. For example, the holes 22 can be 1-5microns wide, or even as small as 2 nanometers. Those skilled in the artcan select the size of the holes 22 based on the electrolyte material 20being used. Ions within the electrolyte material 20 thus can pass freelythrough the holes 22 in the separator 14 to optimize storage capabilityof the super-capacitor 10.

The electrodes 18 may be formed from conventional materials known in theart—preferably a porous solid material. For example, as discussed ingreater detail below, the electrodes 18 may be formed from graphene,which is known to be a porous material with tortuous interior andexterior surfaces. Virtually every surface of the electrode 18 exposedto the electrolyte 20 therefore may be considered part of the surfacearea the capacitor plates represented in the well-known equation:C=ε*(A/D)  (Equation 1),

-   -   where:    -   C is capacitance,    -   ε is a constant,    -   A is the area, and    -   D is distance.

Indeed, those skilled in the art can use other materials to form theelectrode 18, such as activated carbon, carbon aerogel, or carbonnanotubes, to name but a few. Accordingly, discussion of graphene is byexample only and not intended to limit various other embodiments of theinvention.

In a similar manner, the electrolyte 20 can be formed from any of a widevariety of other corresponding materials. For example, electrolyte 20can be formed from an aqueous salt, such as sodium chloride, or a gel,such as a polyvinyl alcohol polymer soaked in a salt. Some embodimentsmay use an ionic liquid, in which ions are in the liquid state at roomtemperature. Although not necessarily aqueous, such electrolytes 20 areknown to be extremely conductive due to the relatively free movement oftheir ions. The inventors believe that such an electrolyte 20 shouldproduce a super-capacitor 10 with a relatively high energy storagecapacity because, as known by those skilled in the art, the energystorage of the capacitor is a function of the square of the voltage.

As noted, the electrolyte 20 preferably is generally integrated withboth the internal and external surfaces of the electrodes 18. Amongother things, the internal surfaces may be formed by tortuous internalchannels and pores within the electrodes 18. The external surfacessimply may be those surfaces visible from the electrode exteriors. Theelectrolyte 20 and noted electrode surfaces thus are considered to forman interface that stores energy.

Depending upon the electrode material, electrons can flow somewhatfreely within the electrodes 18. For example, electrons can flow withingraphene. The electrolyte 20, however, acts as an insulator and thus,does not conduct the electrons from the electrodes 18. In acorresponding manner, the ions in the electrolyte 20 can migratesomewhat freely up to the interfaces with the electrodes 18. Likeelectrons in the electrodes 18, ions in the electrolyte 20 do notmigrate through that interface.

When subjected to an electric field, ions within the electrolyte 20migrate to align with the electric field. This causes electrons andholes in the electrodes 18 to migrate in a corresponding manner,effectively storing charge. For example, in a prescribed electric field,positive ions in the electrolyte 20 may migrate toward a first electrodesurface (e.g., on the top electrode 18), and the negative ions in theelectrolyte 20 may migrate toward a second electrode surface (e.g., onthe bottom electrode 18). In that case, the positive ions near the firstelectrode surface attract electrons (in the electrode 18) toward thatinterface, while the negative ions near the second electrode surfaceattract holes 22 (in the electrode 18) for that interface. The distanceof the ions to the interface plus the distance of the electrons, orholes 22, to the same interface (on the opposite side of the interface)represent distance “d” of Equation 1 above.

Although useful as an electrode material, graphene still does not haveoptimal conductivity properties. Accordingly, illustrative embodimentsalso form a current collector 26 on or as part of the substrate 12 toprovide exterior access to the electrodes 18. Among other things, thecurrent collector 26 may be formed from a highly conductive metal, suchas gold, or a highly doped semiconductor, such as polysilicon. Thoseskilled in the art can select other materials for this purpose.

The super-capacitor 10 has a number of additional features less relevantto this discussion, but worth of mention. For example, it has positiveand negative contacts (not shown, but respectively formed in part by thebase layers of the substrate 12), and a plug 24 for hermetically sealingthe electrolyte 20 in the chamber 16. Moreover, the super-capacitor 10also may have an exterior package, which is not shown in the figures, ormay be considered to form a wafer-level package as shown in FIGS. 1 and2.

FIG. 3 shows a process of fabricating the super-capacitor 10 of FIGS. 1and 2 in accordance with illustrative embodiments of the invention—usingmicromachining processes. It should be noted that this process issubstantially simplified from a longer process that normally would beused to form the super-capacitor 10. Accordingly, the process of formingthe super-capacitor 10 has many steps, such as testing steps oradditional passivation steps, which those skilled in the art likelywould use. In addition, some of the steps may be performed in adifferent order than that shown, or at the same time. Those skilled inthe art therefore can modify the process as appropriate. Moreover, manyof the materials and structures noted (e.g., silicon nitride) are butone of a wide variety of different materials and structures that may beused. Those skilled in the art can select the appropriate materials andstructures depending upon the application and other constraints.Accordingly, discussion of specific materials and structures is notintended to limit all embodiments.

It also should be noted that the process of FIG. 3 is a bulkmicromachining process, which forms a plurality of super-capacitors 10on the same wafer/base at the same time. Although much less efficient,those skilled in the art can apply these principles to a process thatforms only one super-capacitor 10.

The process begins at step 300, which patterns the device layer of asilicon-on-insulator wafer (also known as an “SOI wafer 28”).Specifically, as known by those skilled in the art, an SOI wafer 28 is athree layer wafer structure having an oxide layer 30 (e.g., silicondioxide) between two silicon wafers 32A and 32B. From the perspective ofthe drawings, the top silicon wafer 32A is often referred to as the“device wafer 32A,” while the bottom silicon wafer 32B is often referredto as the “handle wafer 32B.” Accordingly, as shown in FIG. 4, theprocess patterns the device layer of the SOI wafer 28 by forming aconventional etch mask and etching through the openings of the mask.Among other things, the process can perform a dry etch using silicondifluoride (XeF₂). This patterned region within the device layerultimately will form the interior chamber 16 containing the electrodes18 and electrolyte 20.

Next, step 302 insulates the device wafer 32A insulates the device wafer32A. As shown in FIG. 5, some of this insulator contacts the oxide layer30 of the SOI wafer 28. For example, this step may coat the wafer withsilicon nitride 34 (Si₃N₄), which defines an electrode window, togetherwith the photoresist layer 36 to be used in subsequent step 304. Inparticular, as shown in FIG. 6, step 304 deposits a thick photoresistlayer 36 over the wafer, and then patterns the photoresist layer 36 toremove a prescribed portion of the silicon nitride 34, and some of oxidelayer 30 of the SOI wafer 28. Accordingly, this step forms a recess forforming the current collector 26 and the electrode 18.

To that end, step 306 first deposits metal to form a current collectorlayer, which will form the current collector 26. After the depositedmetal cools, the process adds graphene, which forms the electrode 18supported on the substrate 12. In illustrative embodiments, the grapheneis in the form of a plurality of stacked graphene monolayers. This stepconcludes by removing the thick photoresist layer 36 deposited at step304. FIG. 7 schematically shows a cross-sectional view of thewafer/structure (also a “preliminary apparatus”) at the stage of theprocess. The dashed lines show where the photoresist layer 36 waspositioned before it was removed.

After forming the electrode 18, the process continues to step 308,which 1) forms the separator 14, and 2) micromachines holes 22 throughthe separator 14. More specifically, as shown in FIG. 8, the processforms a sacrificial layer 38 within the partial chamber formed by theprevious steps. The sacrificial layer 38, which can be made from anyconventional material, such as silicon dioxide, completely covers theelectrode 18. Next, this step may apply chemical-mechanicalplanarization process, a common wafer grinding process, to expose theuppermost portions of the silicon nitride 34 as shown in FIG. 8.

This step then etches some of the sacrificial layer 38 (in this case,the silicon dioxide), using a conventional etchant, such as hydrofluoricacid. This part of step 308 maintains enough sacrificial material tostill encapsulate the electrode 18. The remaining sacrificial material38 thus forms a support to receive the separator material, which, inthis embodiment, at least in part is formed from silicon nitride. Asnoted above, this separator material (e.g., silicon nitride in thiscase) is substantially impermeable to ions within the electrolyte 20 tobe added at a later step. Finally, step 308 micromachines a plurality ofholes 22 through the silicon nitride to produce the separator 14 shownin FIG. 9 (This figure also has a thinned substrate 12, which is fordrawing purposes only. A thinner substrate 12 is not essential at thisstep). Accordingly, as noted above, the separator holes 22 areconfigured to have a size/dimension and geometry that permits ions ofthe added electrolyte 20 to pass through the separator 14. In theabsence of the holes 22 or some other means, ions could not pass throughthe separator 14.

As noted, this process preferably is performed substantiallysimultaneously with a plurality of other similar structures.Alternatively, this process may be performed serially. In fact, some ofthese structures do not have a separator 14. In any case, step 300 to308 form a plurality of structures (some with separators 14, and somewithout separators 14) that subsequently are used in the remaining stepsof the process.

The process thus continues to step 310, which bonds together two of thewafers shown in FIG. 9 to form the structure of FIG. 11. In thisembodiment, only one of the structures to be boned has the separator 14,while the other does not have the separator 14. To that end, the processfirst covers the silicon nitride separator 14 (of the wafer/structurewith a separator 14) with additional silicon dioxide, and then useschemical mechanical planarization processes to remove the top portion ofthe silicon nitride, consequently exposing the silicon of the devicewafer 32A. This part of step 310 is graphically detailed at FIG. 10. Asimilar process is used to prepare the structures having no separator14. After step 310 prepares both wafers, it then uses conventional waferbonding techniques to bond the two wafers together. This wafer bondingforms the interior chamber 16

At this point in the process, much of the sacrificial material must beremoved to make room for the electrolyte 20 to be added to the interiorchamber 16. To that end, the process continues to step 312, which formsan insulated opening 40 to the chamber 16. Specifically, as shown inFIG. 12, micromachining processes etch an opening 40 through the bottomwafer/structure (which is now thinner) and subsequent more-interiorlayers until the opening 40 reaches the sacrificial oxide in theinterior chamber 16. To protect the oxide layer 30, the process thendeposits silicon nitride on the side walls of the opening 40, thusforming the noted insulated opening 40. FIG. 12 shows the structure atthis point the process.

The insulated opening 40 forms a channel for removing the sacrificialoxide within the interior chamber 16, and then adding electrolyte 20 inits place. Accordingly, step 314 first removes the sacrificial oxidewithin the chamber 16 by conventional means, such as through a vapor orliquid acid etch (e.g., using hydrofluoric acid), to form the structureshown in FIG. 13. Next, step 314 adds electrolyte 20 to the interiorchamber 16.

This interior chamber 16 filled with a liquid electrolyte 20 then isgiven time to cure, depending on the type of electrolyte. Positive ornegative pressure may be applied to better integrate the electrolyte 20with the electrodes 18. Step 316 then seals the opening 40 with anappropriate material to hermetically seal the interior chamber 16. Theplug 24 is but one example of such a seal. FIG. 2 shows thewafer/structure at this stage of the process. Embodiments that do notuse a solid or cured electrolyte 20 (i.e., a liquid electrolyte 20)preferably use an appropriate sealing material that, in the long term,prevents liquid from escaping the interior chamber 16. The processconcludes at step 318, which forms contacts (not shown) on the twosubstrates 12, dices the wafer(s), and then packages the dice asrequired by the application.

As noted above, step 310 may bond together two identicalwafers/structures that both have separators 14. In that case, the finaldevice may look more like the die/structure of FIG. 14, which has adouble-separator design. Such a design should improve reliability andsafety.

Some embodiments also may apply to a super-capacitor 10 havingside-by-side/coplanar electrodes 18, such as that shown in FIG. 15. Inthis case, a single substrate 12 may support electrodes 18 withinseparate but connected interior chambers 16 formed by a cap wafer 41(e.g., a silicon wafer). Specifically, the chambers have separators 14(e.g., formed from nitride) with pre-formed holes 22 that communicatewith through-holes 42 extending through the substrate 12 and cap wafer41. FIG. 15 also shows through-holes 42 across cross-section A-A.Various embodiments have electrolyte 20 extending through the separatorholes 22 and through-holes 42.

Accordingly, illustrative embodiments form robust and reliablesuper-capacitors 10 using a separator 14 formed from strong materialsnot previously used in super-capacitor art (to the knowledge of theinventors). Such materials now are available because the affirmativelyformed holes 22 through the separator 14 permit the ions to traverse theentire interior chamber region containing the electrolyte 20.

Although the above discussion discloses various exemplary embodiments ofthe invention, it should be apparent that those skilled in the art canmake various modifications that will achieve some of the advantages ofthe invention without departing from the true scope of the invention.

What is claimed is:
 1. A super-capacitor comprising: a first substrateand a second substrate; a first electrode supported by the firstsubstrate; a second electrode supported by the second substrate; thefirst substrate bonded to the second substrate to form an interiorchamber; a first separator between the first electrode and the secondelectrode within the interior chamber, the first separator having aplurality of micromachined etch holes; electrolyte, having ions, withinthe interior chamber and in contact with the first and secondelectrodes, the first separator micromachined etch holes being sized topermit the ions to pass through the micromachined etch holes.
 2. Thesuper-capacitor as defined by claim 1 wherein each of the first andsecond electrodes comprises a porous solid material.
 3. Thesuper-capacitor as defined by claim 2 wherein each of the first andsecond electrodes comprises a plurality of graphene monolayers.
 4. Thesuper-capacitor as defined by claim 1 further comprising a secondseparator between the first separator and the second electrode.
 5. Thesuper-capacitor as defined by claim 1 wherein the electrolyte comprisesa cured gel electrolyte.
 6. The super-capacitor as defined by claim 1wherein the first separator comprises nitride or parylene.
 7. Thesuper-capacitor as defined by claim 1 wherein the first separator isformed from a material that is substantially ion impermeable to the ionswithin the electrolyte.
 8. A super-capacitor comprising: a firstsubstrate and a second substrate that together form at least a portionof a die; a first electrode and a second electrode, the first and secondelectrodes being spaced apart and being between the first and secondsubstrates, the die forming an interior chamber; a separator between thefirst electrode and the second electrode within the interior chamber,the separator having a plurality of micromachined etch holes;electrolyte, having ions, within the interior chamber and in contactwith the first and second electrodes, the separator micromachined etchholes being sized to permit the ions to pass through the micromachinedetch holes.
 9. The super-capacitor as defined by claim 8 wherein each ofthe first and second electrodes comprises a porous solid material. 10.The super-capacitor as defined by claim 9 wherein each of the first andsecond electrodes comprises a plurality of graphene monolayers.
 11. Thesuper-capacitor as defined by claim 8 wherein the separator comprises afirst separator and a second separator between the first and secondelectrodes.
 12. The super-capacitor as defined by claim 8 wherein theelectrolyte comprises a cured gel electrolyte.
 13. The super-capacitoras defined by claim 8 wherein the separator comprises nitride orparylene.
 14. The super-capacitor as defined by claim 8 wherein theseparator is formed from a material that is substantially ionimpermeable to the ions within the electrolyte.
 15. A super-capacitorcomprising: a first substrate and a second substrate; a first electrodeand a second electrode, the first and second electrodes being spacedapart and positioned between the first and second substrates; means forinterior containing electrolyte between the first and second substrates;means for separating the first electrode and the second electrode withinthe interior containing means; electrolyte, having ions, within theinterior containing means and in contact with the first and secondelectrodes, the separating means having micromachined etched means forpermitting the ions to pass through the separating means.
 16. Thesuper-capacitor as defined by claim 15 wherein the permitting meanscomprises a plurality of micromachined etch holes through the separatingmeans.
 17. The super-capacitor as defined by claim 15 wherein each ofthe first and second electrodes comprises a porous solid material. 18.The super-capacitor as defined by claim 17 wherein each of the first andsecond electrodes comprises a plurality of graphene monolayers.
 19. Thesuper-capacitor as defined by claim 15 wherein the electrolyte comprisesa cured gel electrolyte.
 20. The super-capacitor as defined by claim 15wherein the separating means is formed from a material that issubstantially ion impermeable to the ions of the electrolyte.